This invention relates in general to the field of test fixtures and calibration standards, and, in particular, to a probeable substrate substitute for a calibration standard and test fixture.
Accurately measuring and characterizing devices and circuits has often proven difficult since such components do not connect directly with measurement equipment. A test fixture is often needed to transition between the device and test set. Hence, an electrical measurement of a device in a test fixture includes both device parameters as well as fixturing effects. To determine only the device parameters, the fixture must be characterized and its contribution mathematically removed from the overall measurement. Since such fixturing is complicated and contains electrical discontinuities, it is difficult and sometimes impossible to effectively characterize fixture parameters. Such limitations on the effective characterization of fixture parameters, in turn, place limitations on how accurately device parameters can be determined.
In some microwave monolithic integrated circuits (MMICs), the devices or circuits can be fabricated with probe connections which allow commercial test equipment to probe for electrical parameters directly on the device. Probeable devices improve the accuracy of determining device parameters since the probes can be accurately calibrated and their effects removed from the measured data. Unfortunately, however, many devices, including schottky barrier diodes, gallium arsenide (GaAs) metal-schottky field effect transistors (GaAs MESFETs), and certain other MMICs do not allow measurement by direct probing. The only way to measure the electrical characteristics of unprobeable devices is to measure them as they are embedded in the fixture.
Thus, what is needed is a practical, economical method for accurately characterizing devices which are unsuitable for direct probing. It is desirable to provide for a calibration standard and test fixture substitute which includes RF connections which allow probe contact with commercial test equipment. It is additionally desirable if typical calibration standards, e.g., load-reflect-through, through-reflect-line, etc. are incorporated into the probeable substrate.